Re: [PATCH v2] PCI: qcom: fix IPQ8074 Gen2 support

[Robert Marko]

On Tue, 21 Jun 2022 at 23:43, Bjorn Helgaas <helgaas@xxxxxxxxxx> wrote:
>
> On Tue, Jun 21, 2022 at 11:05:17PM +0200, Robert Marko wrote:
> > On Tue, 21 Jun 2022 at 22:32, Bjorn Helgaas <helgaas@xxxxxxxxxx> wrote:
> > > On Tue, Jun 21, 2022 at 01:23:30PM +0200, Robert Marko wrote:
> > > > IPQ8074 has one Gen2 and one Gen3 port, currently the Gen2 port will
> > > > cause the system to hang as its using DBI registers in the .init
> > > > and those are only accesible after phy_power_on().
> > >
> > > Is the fact that IPQ8074 has both a Gen2 and a Gen3 port relevant to
> > > this patch?  I don't see the connection.
> >
> > Not really, I can remove it from the description as this only affects the Gen2
> > port, Gen3 support is dependant on the IPQ6018 support getting merged as
> > it uses the same controller.
>
> Great, I think unrelated details confuse things.
>
> > > I see that qcom_pcie_host_init() does:
> > >
> > >   qcom_pcie_host_init
> > >     pcie->cfg->ops->init(pcie)
> > >     phy_power_on(pcie->phy)
> > >     pcie->cfg->ops->post_init(pcie)
> > >
> > > and that you're moving DBI register accesses from
> > > qcom_pcie_init_2_3_3() to qcom_pcie_post_init_2_3_3().
> > >
> > > But I also see DBI register accesses in other .init() functions:
> > >
> > >   qcom_pcie_init_2_1_0
> > >   qcom_pcie_init_1_0_0      (oddly out of order)
> > >   qcom_pcie_init_2_3_2
> > >   qcom_pcie_init_2_4_0
> > >
> > > Why do these accesses not need to be moved?  I assume it's because
> > > pcie->phy is an optional PHY and phy_power_on() does nothing on those
> > > controllers?
> >
> > As far as I could figure out from QCA-s 5.4 kernel, various commits,
> > and QCA-s attempts to solve this already upstream the Gen2
> > controller in IPQ8074 is a bit special and requires the PHY to be
> > powered on before DBI could be accessed or else the board will hang
> > as it does for me.
> >
> > I can only assume that this is an IPQ8074-specific quirk and other
> > IP-s are not affected like this, so they were not broken.
>
> > > Whatever the reason, I think the DBI accesses should be done
> > > consistently in .post_init().  I see that Dmitry's previous patches
> > > removed all those .post_init() functions, but I think the consistency
> > > is worth having.
> > >
> > > Perhaps we could reorder the patches so this patch comes first, moves
> > > the DBI accesses into .post_init(), then Dmitry's patches could be
> > > rebased on top to drop the clock handling?
> > >
> > > > So solve this by splitting the DBI read/writes to .post_init.
> >
> > I am open to anything to get this fixed properly, you are gonna need
> > to point me in the right direction as I am really new to PCI.
>
> Unless there's a reason *not* to move the DBI accesses for other
> variants, I think we should move them all to .post_init().  Otherwise
> it's just magic -- there's no indication in the code about why IPQ8074
> needs to be different from all the rest.

Hi Bjorn,
I am not sure how to do it properly, especially for the 2.1.0 IP that
IPQ8064 uses
and that is already filled with tweaks to get it properly working.

As far as I can tell, the reason why it works for all of the others is that they
dont use a PHY driver at all (2.1.0 in IPQ8064 and 2.4.0 in IPQ4019),
1.1.0 in APQ8084 appears to be unused completely as its compatible is not
used in any of the DTS-es.
2.3.2 in MSM8996 and MSM8998 also use QMP, so I am not sure why these work.

>
> a0fd361db8e5 appeared in v5.11, so presumably IPQ8074 has been broken
> since then?  Are there any problem report URLs or references to the
> attempts you mentioned above that we could include here?

It has been broken since then, it worked on 5.10 when I started poking around
IPQ8074 and after backporting the 5.11 commits to get the Gen3 port working
it stopped working, and I traced that down to hanging after a DBI write.

This appears to be QCA-s attempt to always power on the PHY before the init:
https://patchwork.kernel.org/project/linux-pci/patch/1596036607-11877-6-git-send-email-sivaprak@xxxxxxxxxxxxxx/

>
> Since folks may want to backport the fix to v5.11, I'd probably do
> this patch by itself to make the backport easier, then add a second
> patch to move the DBI accesses for all the other variants.
>
> My personal opinion is that you should do this based on v5.19-rc1, and
> then we can rebase Dmitry's patches on top.  That would make all the
> patches simpler and it would make yours easier to backport.  But
> that's the sort of thing Dmitry, Stanimir, Andy, and Bjorn A. could
> weigh in on.

This patch applies to 5.19 as well, though I will send a v4 with the
updated description.
Like, I said, I am not sure how to move DBI accesses in other IP-s
without breaking them.

Regards,
Robert
>
> Bjorn H.